1. Technical Field
This invention relates to semiconductor devices and more particularly, to an improved dielectric layer and method of formation thereof.
2. Description of the Related Art
Semiconductor memory cells include capacitors accessed by transistors to store data. Data is stored as a high or low bit depending on the state of the capacitor. The capacitor's charge or lack of charge indicates a high or low when accessed to read data, and the capacitor is charged or discharged to write data thereto.
Deep trench (DT) capacitors are among the types of capacitors used in semiconductor memories. Deep trench capacitors are typically buried within a semiconductor substrate of the device adjacent to or below an access transistor.
For optimum performance of semiconductor memory devices, such as dynamic random access memories (DRAM), the capacitance C of the storage trench capacitor should be maximized while the charge leakage to areas surrounding the capacitor should be minimized. These requirements dictate the use of high quality dielectric materials interposed between the plates of the capacitor.
The capacitance of the trench capacitor is given by the equation, C=.di-elect cons..multidot.A/d, where C is the capacitance, .di-elect cons. is the dielectric constant of the material interposed between the plates of the capacitor, A is the area of the capacitor plates, and d is the thickness of the dielectric material separating the plates of the capacitor.
In conventional trench capacitor fabrication, an Oxinitride is typically used as the dielectric material. Oxinitride materials are highly compatible with current deep trench capacitor manufacturing processes and materials and are stable over the high temperature treatments incurred during the formation of deep trench capacitors (up to 1100.degree. C.). However, Oxinitrides typically exhibit a dielectric of about 7, which is insufficient to achieve the required capacitances without changing the geometry of the capacitor in a manner that degrades the leakage characteristics of the capacitor.
Therefore, there remains a need for a method and apparatus for increasing the capacitance of a deep trench capacitor without degrading the leakage characteristics of the device. As seen in the above equation, this objective can be obtained by using a dielectric material having a higher dielectric constant .di-elect cons. which is compatible with the formation process of deep trench capacitors.